This upgrade tip applies to the inexperienced user.Before you upgrade restore your CMS back to it's core state. This will help to rule out any possible issues related to none core blocks, modules and themes later.

BACK UP , BACK UP, and then BACK UP

Go to Admin.php

Activate maintenance mode

Theme
System/
Where it says, "The default theme for my site": |default|
(change it to the core theme, titled, default. If you have removed this you will need to reinstall it. Before you upgrade.)

Modules
General/Modules/
Deactivate (Uncheck) all non-core modules. You do not have to uninstall them, just deactivate them.
Where it says, "Set as Home", choose the core, News module (if you had a non-core module as your homepage).

Blocks
General/Blocks
Deactivate (uncheck) all non-core blocks or blocks you have modified from the original core state.

After you have upgraded make sure you check with the developers of any non-core themes, modules and blocks to make sure they are compliant
with 9.2.1. version before you activate them.
As stated in the install documentation.
What to do if you didn't read this and having problemsExtreme suggestion

Restore your back up and start over!

Note: Please be advised these are only suggestions and what worked for me. As always, following directions from the documentation included with the software is advised.